1. Field of the Invention
This invention relates to an information recording technique to an optical disc.
2. Description of Related Art
When information is recorded on an optical disc, various controls are executed in order to form pits (recording marks) of accurate shapes corresponding to information to be recorded. Some of them detect a return light from an optical disc which is generated by irradiating a recording laser beam to the optical disc, and execute various controls for recording, based on the return light quantity.
As an example of such controls, there is known ROPC (Running Optimum Power Control) which controls a recording power so as to always form constantly-shaped pits during recording. The ROPC detects a return light from an optical disc while a recording laser beam is irradiated onto the disc, and controls the recording power of the laser beam based on the level of the return light. A recording power control by ROPC can be applied to optical discs such as CD-R (Compact Disc-Recordable) DVD-R and DVD-RW.
However, in cases of DVD-R and DVD-RW, which are different from CD-R, there is a problem that the return light quantity from the disc varies due to the existence of prepits because prepits such as land-prepits (LPP) are formed on a recording surface of the disc. Specifically, grooves serving as recording tracks and lands are alternately formed in a radial direction on the recording surface of DVD-R and DVD-RW. On the lands, LPPs including addresses and other information are formed according to a predetermined rule. Return light quantity of a recording laser beam which is used to the control such as ROPC varies by the existence of the LPPs. The problem is that a current pit forming condition is recognized incorrectly and proper recording power adjustment can not be executed because of this variation of the return light quantity.
This problem is not limited to the case of ROPC. Namely, in the case of other controls which are executed by using the return light quantity of the recording laser beam during recording, accurate controls cannot be executed because the existence of prepits varies the return light quantity.